(WGL) windows 中的OpenGL

在这里主要介绍在windows窗体应用程序中使用OpenGL  API；

OpenGL与windows窗体的协调工作是通过渲染环境来实现的。

在这里首先明白两个名词：渲染环境与设备环境

设备环境是由windows保存的一种数据结构，用来记录、描述图形设备的一些属性值；

渲染环境是由OpenGL提供的API来进行创建，渲染环境也是记录保存一些与绘图有关的属性值；

渲染环境与设备环境的设置应该保持一致。

下面结合一个简单的例子说明OpenGL与windows窗体的结合及应用：

首先需要说明的是，在这里创建应用程序之初，应选择窗体应用程序，否则就需要对项目属性进行设置。设置方法

下面言归正传对程序进行程序的结构进行说明：

1、利用windows API创建一个窗体  代码如下：

WNDCLASSEX windowClass;     // window class
    HWND       hwnd;            // window handle
    MSG        msg;             // message
    DWORD      dwExStyle;       // Window Extended Style
    DWORD      dwStyle;         // Window Style
    RECT       windowRect;

    g_glRender = new CGfxOpenGL;

    windowRect.left = (long)0;                        // Set Left Value To 0
    windowRect.right = (long)windowWidth; // Set Right Value To Requested Width
    windowRect.top = (long)0;                         // Set Top Value To 0
    windowRect.bottom = (long)windowHeight;   // Set Bottom Value To Requested Height

    // fill out the window class structure
    windowClass.cbSize = sizeof(WNDCLASSEX);
    windowClass.style = CS_HREDRAW | CS_VREDRAW;
    windowClass.lpfnWndProc = MainWindowProc;
    windowClass.cbClsExtra = 0;
    windowClass.cbWndExtra = 0;
    windowClass.hInstance = hInstance;
    windowClass.hIcon = LoadIcon(NULL, IDI_APPLICATION);  // default icon
    windowClass.hCursor = LoadCursor(NULL, IDC_ARROW);      // default arrow
    windowClass.hbrBackground = NULL;                             // don't need background
    windowClass.lpszMenuName = NULL;                             // no menu
    windowClass.lpszClassName = "GLClass";
    windowClass.hIconSm = LoadIcon(NULL, IDI_WINLOGO);      // windows logo small icon

    // register the windows class
    if (!RegisterClassEx(&windowClass))
        return 0;

    if (fullscreen)                             // fullscreen?
    {
        DEVMODE dmScreenSettings;                   // device mode
        memset(&dmScreenSettings, 0, sizeof(dmScreenSettings));
        dmScreenSettings.dmSize = sizeof(dmScreenSettings);
        dmScreenSettings.dmPelsWidth = windowWidth;            // screen width
        dmScreenSettings.dmPelsHeight = windowHeight;           // screen height
        dmScreenSettings.dmBitsPerPel = windowBits;             // bits per pixel
        dmScreenSettings.dmFields = DM_BITSPERPEL | DM_PELSWIDTH | DM_PELSHEIGHT;

        // 
        if (ChangeDisplaySettings(&dmScreenSettings, CDS_FULLSCREEN) != DISP_CHANGE_SUCCESSFUL)
        {
            // setting display mode failed, switch to windowed
            MessageBox(NULL, "Display mode failed", NULL, MB_OK);
            fullscreen = FALSE;
        }
    }

    if (fullscreen)                             // Are We Still In Fullscreen Mode?
    {
        dwExStyle = WS_EX_APPWINDOW;                  // Window Extended Style
        dwStyle = WS_POPUP;                       // Windows Style
        ShowCursor(FALSE);                      // Hide Mouse Pointer
    }
    else
    {
        dwExStyle = WS_EX_APPWINDOW | WS_EX_WINDOWEDGE;   // Window Extended Style
        dwStyle = WS_OVERLAPPEDWINDOW;                    // Windows Style
    }

    AdjustWindowRectEx(&windowRect, dwStyle, FALSE, dwExStyle);     // Adjust Window To True Requested Size

    // class registered, so now create our window
    hwnd = CreateWindowEx(NULL,                                 // extended style
        "GLClass",                          // class name
        "BOGLGP - Chapter 2 - OpenGL Application",      // app name
        dwStyle | WS_CLIPCHILDREN |
        WS_CLIPSIBLINGS,
        0, 0,                               // x,y coordinate
        windowRect.right - windowRect.left,
        windowRect.bottom - windowRect.top, // width, height
        NULL,                               // handle to parent
        NULL,                               // handle to menu
        hInstance,                          // application instance
        NULL);                              // no extra params

    hDC = GetDC(hwnd);

    // check if window creation failed (hwnd would equal NULL)
    if (!hwnd)
        return 0;

    ShowWindow(hwnd, SW_SHOW);          // display the window
    UpdateWindow(hwnd);                 // update the window

说明一下在这里fullscreen 变量设置为false  否则如果不加入OpenGL程序就会出错，对创建窗体程序不太熟悉的原因，感觉应该是需要重写窗体的事件。

下面一个与OpenGL无关的创建一个窗体的程序，就算是学习windows 窗体应用程序的相关知识吧!

#include <Windows.h>

bool exiting = false;
long windowWidth = 800;
long windowHeight = 600;
long windowBits = 32;
bool fullscreen = false;
HDC hDC;

void SetupPixelFormat(HDC hDC)  //设置像素格式
{
    int pixelFormat;

    PIXELFORMATDESCRIPTOR pfd =
    {
        sizeof(PIXELFORMATDESCRIPTOR),  // size
        1,                          // version
        PFD_SUPPORT_OPENGL |        // OpenGL window
        PFD_DRAW_TO_WINDOW |        // render to window
        PFD_DOUBLEBUFFER,           // support double-buffering
        PFD_TYPE_RGBA,              // color type
        32,                         // prefered color depth
        0, 0, 0, 0, 0, 0,           // color bits (ignored)
        0,                          // no alpha buffer
        0,                          // alpha bits (ignored)
        0,                          // no accumulation buffer
        0, 0, 0, 0,                 // accum bits (ignored)
        16,                         // depth buffer
        0,                          // no stencil buffer
        0,                          // no auxiliary buffers
        PFD_MAIN_PLANE,             // main layer
        0,                          // reserved
        0, 0, 0,                    // no layer, visible, damage masks
    };

    pixelFormat = ChoosePixelFormat(hDC, &pfd);
    SetPixelFormat(hDC, pixelFormat, &pfd);
}
/*当窗体触发任何一个事件时，便会调用此函数*/
LRESULT CALLBACK MainWindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    static HDC hDC;
    static HGLRC hRC;
    int height, width;

    // dispatch messages
    switch (uMsg)
    {
    case WM_CREATE:         // window creation
        hDC = GetDC(hWnd);
        SetupPixelFormat(hDC);
        //SetupPalette();
        //hRC = wglCreateContext(hDC);
        //wglMakeCurrent(hDC, hRC);
        break;

    case WM_DESTROY:            // window destroy
    case WM_QUIT:
    case WM_CLOSE:                  // windows is closing

        // deselect rendering context and delete it
        //wglMakeCurrent(hDC, NULL);
        //wglDeleteContext(hRC);

        // send WM_QUIT to message queue
        PostQuitMessage(0);
        break;

    case WM_SIZE:
        height = HIWORD(lParam);        // retrieve width and height
        width = LOWORD(lParam);


        break;

    case WM_ACTIVATEAPP:        // activate app
        break;

    case WM_PAINT:              // paint
        PAINTSTRUCT ps;
        BeginPaint(hWnd, &ps);
        EndPaint(hWnd, &ps);
        break;

    case WM_LBUTTONDOWN:        // left mouse button
        break;

    case WM_RBUTTONDOWN:        // right mouse button
        break;

    case WM_MOUSEMOVE:          // mouse movement
        break;

    case WM_LBUTTONUP:          // left button release
        break;

    case WM_RBUTTONUP:          // right button release
        break;

    case WM_KEYUP:
        break;

    case WM_KEYDOWN:
        int fwKeys;
        LPARAM keyData;
        fwKeys = (int)wParam;    // virtual-key code 
        keyData = lParam;          // key data 

        switch (fwKeys)
        {
        case VK_ESCAPE:
            PostQuitMessage(0);
            break;
        default:
            break;
        }

        break;

    default:
        break;
    }
    return DefWindowProc(hWnd, uMsg, wParam, lParam);
}
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nShowCmd)
{
    WNDCLASSEX windowClass;     // window class
    HWND       hwnd;            // window handle
    MSG        msg;             // message
    DWORD      dwExStyle;       // Window Extended Style
    DWORD      dwStyle;         // Window Style
    RECT       windowRect;

    windowRect.left = (long)0;                        // Set Left Value To 0
    windowRect.right = (long)windowWidth; // Set Right Value To Requested Width
    windowRect.top = (long)0;                         // Set Top Value To 0
    windowRect.bottom = (long)windowHeight;   // Set Bottom Value To Requested Height

    // fill out the window class structure
    windowClass.cbSize = sizeof(WNDCLASSEX);
    windowClass.style = CS_HREDRAW | CS_VREDRAW;
    windowClass.lpfnWndProc = MainWindowProc;    //当窗体触发任何一个事件时，便会调用该函数  
    windowClass.cbClsExtra = 0;
    windowClass.cbWndExtra = 0;
    windowClass.hInstance = hInstance;
    windowClass.hIcon = LoadIcon(NULL, IDI_APPLICATION);  // default icon
    windowClass.hCursor = LoadCursor(NULL, IDC_ARROW);      // default arrow
    windowClass.hbrBackground = NULL;                             // don't need background
    windowClass.lpszMenuName = NULL;                             // no menu
    windowClass.lpszClassName = "GLClass";
    windowClass.hIconSm = LoadIcon(NULL, IDI_WINLOGO);      // windows logo small icon

    // register the windows class
    if (!RegisterClassEx(&windowClass))
        return 0;
    dwExStyle = WS_EX_APPWINDOW | WS_EX_WINDOWEDGE;   // Window Extended Style
    dwStyle = WS_OVERLAPPEDWINDOW;                    // Windows Style
    AdjustWindowRectEx(&windowRect, dwStyle, FALSE, dwExStyle);     // Adjust Window To True Requested Size

    // class registered, so now create our window
    hwnd = CreateWindowEx(NULL,                                 // extended style
        "GLClass",                          // class name
        "BOGLGP - Chapter 2 - OpenGL Application",      // app name
        dwStyle | WS_CLIPCHILDREN |
        WS_CLIPSIBLINGS,
        0, 0,                               // x,y coordinate
        windowRect.right - windowRect.left,
        windowRect.bottom - windowRect.top, // width, height
        NULL,                               // handle to parent
        NULL,                               // handle to menu
        hInstance,                          // application instance
        NULL);                              // no extra params

    hDC = GetDC(hwnd);

    // check if window creation failed (hwnd would equal NULL)
    if (!hwnd)
        return 0;

    ShowWindow(hwnd, SW_SHOW);          // display the window
    UpdateWindow(hwnd);                 // update the window
    while (true)
    {

    }
    return 1;
}

2、接下来是利用OpenGL API创建渲染环境并绘图

这个主要是利用了一个渲染类，渲染类中的程序大都在OpenGL基础中讲解过

下面就看OpenGL的渲染应该写在什么地方

OpenGL程序写在创建完窗体程序后的一个循环中。代码如下：

g_glRender->Init();

    while (!exiting)
    {
        g_glRender->Prepare(0.0f);
        g_glRender->Render();
        SwapBuffers(hDC);

        while (PeekMessage(&msg, NULL, 0, 0, PM_NOREMOVE))
        {
            if (!GetMessage(&msg, NULL, 0, 0))
            {
                exiting = true;
                break;
            }

            TranslateMessage(&msg);
            DispatchMessage(&msg);
        }
    }

    delete g_glRender;

那么设备环境与渲染环境是如何协调工作的呢？

这个是在创建窗体之初（还未display）时设定的，写在了窗体的事件回调函数中MainWindowProc

switch (uMsg)
    {
    case WM_CREATE:         // window creation
        hDC = GetDC(hWnd);  //设备环境句柄
        SetupPixelFormat(hDC);  //设定设备环境像素格式
        hRC = wglCreateContext(hDC);  //创建渲染环境  但返回值是一个句柄  而不是渲染环境  通过句柄将该渲染环境作为参数传递给其他函数
        //创建完渲染环境之后 需要使其生效
                wglMakeCurrent(hDC, hRC);
        break;
        ……
        ……
        }        

OK了 ，这一节就写到这儿吧 ，感觉还是没有完全写清楚，但还是貌似明白了不少东西……